1. Field of the Invention
The present invention relates to a zoom lens barrel, and more precisely relates to a selectable assembling device for a zoom lens barrel in which deterioration of optical properties due to a manufacturing error or assembly error can be minimized. The present invention also relates to a guide device for a flexible printed circuit board extending from a shutter block thereof.
2. Description of the Related Art
In general, in a zoom lens barrel, a plurality of lens frames (lens groups) which are guided to linearly move are linearly moved in the optical axis direction in accordance with the rotation of a cam barrel having cam grooves with predetermined tracks. To increase the displacement of the lens groups, in most cases, the cam barrel is connected to a stationary barrel via helicoids. In general, the cam barrel and the stationary barrel are screw-engaged at only one assembly engagement position in the circumferential direction. Therefore, the assembly engagement position in the circumferential direction of the cam barrel and the lens frames (lens groups) which are guided to linearly move occurs at only one position.
In a conventional zoom lens barrel as mentioned above, since the components thereof inevitably have a manufacturing error, in general, optical performance characteristics expected on design cannot be obtained. In particular, in the prior art in which the assembly engagement position in the circumferential direction of the lens frame which are guided to linearly move and the cam barrel occurs at only one position, if the zoom lens barrel is assembled so that the manufacturing errors of the components are cumulated at the one assembly engagement position, there is no way to eliminate the cumulative manufacturing error.
In particular, in a digital camera, an image is formed on a CCD whose size is significantly smaller than the size of a picture plane of a silver-halide film camera, and hence, the required accuracy of the lens in a digital camera is about ten times higher than in a silver-halide film camera. For example, for the same angle of view, the focal length of the lens is reduced as the image size is reduced, and accordingly, the lenses, the lens frames and other components are all reduced in size. Consequently, influence on a lens system by the same dimensional error, e.g., an error of 10 xcexcm, is exaggerated in a digital camera. Namely, an error which is negligible in a silver-halide film camera from the viewpoint of optical performance is not negligible in a digital camera. In particular, in a lens system of a digital camera, the deviation or inclination of the lens axes of the lens groups is more serious than the error of the plurality of lens frames (lens groups) in the optical axis direction, in view of the influence on the optical performance thereof.
In a zoom lens barrel for a lens shutter type camera, an exposure controlling shutter block is indispensable. In expensive digital cameras, in general, a shutter block is provided which is chiefly adapted to close a photographing light path after the shutter is released to thereby prevent unnecessary electric charges from being accumulated in the CCD. The shutter block is secured to any one of lens groups which are reciprocally moved in the optical axis direction in accordance with the zooming operation in a zoom lens barrel.
A flexible printed circuit board which is adapted to supply operation signals to the shutter block changes the position thereof in accordance with the zooming operation. To this end, a guide device for the printed circuit board (which permits the circuit board to extend or deform) must be provided. Various guide devices for various structures of the zoom lens barrel have been proposed.
It is an object of the present invention to provide an selectable assembling device in which a plurality of lens groups are reciprocally moved in the optical axis direction by the rotation of a cam barrel having a cam groove, wherein an assembly position can be selected in which deviation of the lens axes of the lens groups tends not to occur even if the components of the lens barrel have an manufacturing error.
It is another object of the present invention to provide a guide device which guides a flexible circuit board which extends from a shutter block, without interfering with the zoom mechanism and without reducing the mechanical strength of the components in a zoom lens barrel.
According to an aspect of the present invention, a selectable assembling device of a zoom lens barrel is provided, including a stationary barrel having a female helicoid and linear guide grooves, the linear guide grooves being formed across the female helicoid extending parallel to the optical axis of the zoom lens barrel, the linear guide grooves spaced at 120 degree intervals about the axis of the stationary barrel, wherein a portion of each of the plurality of linear guide grooves includes an introducing groove formed by cutting a portion of the female helicoid, a cam ring which is provided on the outer peripheral surface thereof with a male helicoid which is engaged with the female helicoid of the stationary barrel, the cam ring including bottomed cam grooves provided at 120 degree intervals about the axis of the cam ring on the inner peripheral surface thereof, the cam ring being rotated with respect to the stationary barrel which does not rotate; a linear guide barrel which is provided with linear guide projections and linear guide slots spaced at 120 degree intervals about the axis of the linear guide barrel, the linear guide projections being engaged in the linear guide grooves of the stationary barrel, the linear guide barrel and the cam ring being coupled so that the linear guide barrel is rotatable relative to the optical axis and moveable in the optical axis direction together with the cam ring; and a plurality of lens frames which are provided with sliding projections, that are spaced at 120 degree intervals about the optical axis, which are engaged in the linear guide slots of the linear guide barrel, each of the sliding projections including a cam follower thereon which is fitted in a corresponding bottomed cam groove of the cam ring. Upon assembly, a first relative angular position of assembly for the cam ring and the linear guide barrel can be selected from among three circumferential positions spaced at 120 degree intervals about common axes of the cam ring and the linear guide barrel.
Preferably, the assembly of the cam ring and the linear guide barrel is constructed so that when the male helicoid of the cam ring is engaged with the female helicoid of the stationary barrel, the linear guide projections of the linear guide barrel are engaged in the linear guide grooves of the stationary barrel at a second relative angular position selected from three circumferential positions spaced at 120 degree intervals about common axes of the linear guide barrel and the stationary barrel while maintaining the first relative angular position.
Preferably, the cam ring is provided with identification indicia which are adapted to identify the three circumferential positions of the first relative angular position.
In an embodiment, the first relative angular position is a combination of a third relative angular position and a fourth relative angular position. The sliding projections of the plurality of lens frames are engaged in the linear slots of the linear guide at the third relative angular position selected from three circumferential positions spaced at 120 intervals about the optical axis; and the cam followers of the sliding projections are engaged in the bottomed cam grooves of the cam ring at the fourth relative angular position selected from three circumferential positions spaced at 120 degree intervals about the axis of the cam ring.
According to another aspect of the present invention, a guide device for guiding a flexible circuit board of a zoom lens barrel is provided, including a plurality of lens groups which are guided to move in an optical axis direction of the zoom lens barrel to vary a focal length of a photographing optical system; a shutter block secured to any one of the lens groups; a rotational barrel; a cam ring which is located inside the rotational barrel and which is rotated by the rotation of the rotational barrel to move the lens groups in the optical axis direction; a flexible circuit board which is connected at one end thereof to the shutter block; and a flexible circuit board insertion slot formed in the rotational barrel and extending in the circumferential direction of the rotational barrel. The flexible circuit board extends rearward from the shutter block, bends forward at the rear end of the cam ring, extends forward between the rotational barrel and the cam ring, and extends to the outside of the rotational barrel through the flexible circuit board insertion slot of the rotational barrel.
In an embodiment, the rotational barrel is provided on the inner peripheral surface thereof with a plurality of inward projections that are spaced in the circumferential direction;
wherein the cam ring is provided on the outer peripheral surface thereof with a plurality of axially extending rotation transmission grooves that are spaced in the circumferential direction, wherein each rotation transmission groove can be engaged with each respective the inward projections. The flexible circuit board insertion slot of the rotational barrel is located behind the inward projections with respect to the optical axis.
In an embodiment, the inward projections of the rotational barrel are spaced from one another at 120 degree intervals, wherein the rotation transmission grooves of the cam ring are spaced from one another at 120 degree intervals, and wherein the flexible circuit board insertion slot of the rotational barrel extends for at least 120 degrees about the optical axis.
In an embodiment, the cam ring is connected to a stationary barrel via helicoids so as to rotate and move in the optical axis direction.
In an embodiment, the rotational barrel is connected to the stationary barrel by a thread whose lead is smaller than that of the helicoids so as to rotate and move in the optical axis direction.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2000-22742 (filed on Jan. 31, 2000) and Japanese Patent Application No.2000-24042 (filed on Feb. 1, 2000) which are expressly incorporated herein by reference in their entireties.